The present invention relates generally to bushings for forming fibers from a fluid material, such as glass at an elevated temperature and more particularly, to an improved manner of reinforcing a bushing tip plate to extend the service life thereof.
Various types of bushings or bushing assemblies for forming fibers or filaments from a fluid material, such as glass at an elevated temperature, are known in the art. Usually, the bushing or bushing assembly includes a rectangular bushing body having sidewalls and end walls. Together, the side and end walls serve as a frame for supporting or carrying one or more, often elongated plate-like structures, typically formed of platinum or alloys thereof, having a plurality of small orifices or xe2x80x9ctips.xe2x80x9d These tips receive the molten material as it passes through the bushing body from an upstream source, such as a forehearth. To assist in keeping the material in a molten state as it enters and passes through these tips, the plates are heated, usually by electrically coupling them to a source of high current, such as a transformer. As molten glass material streams exit the tips, they are mechanically drawn to form continuous fibers which are wound onto mandrels or creels or directly chopped for later processing or use. A detailed description of the basic apparatus and methodology used is found in commonly assigned U.S. Pat. No. 5,709,727 to Bobba and U.S. Pat. No. 3,920,430 to Carey, the disclosures of which are incorporated herein by reference.
To improve the output and efficiency of the overall fiber-forming operation, it is of course desirable to maximize the number of fibers created by the tip plate. To do so, a tip plate can in theory be made infinitely large in both the width and length dimensions. However, several well-recognized problems arise, especially when the width dimension of a tip plate is significantly increased relative to the length dimension.
Perhaps the most prevalent problem resulting from increasing the dimensions of the tip plate, and in particular, the width dimension, to the degree necessary to realize a significant increase in fiber output is a sharp reduction in the service life. The tip plate is normally rectangular in top plan view, with its four side edges welded directly to the opposed side and end walls of the rectangular bushing body. When the width dimension of the tip plate increases relative to the length dimension, the plate essentially acts as a simple beam supported at the sides and ends, with no direct support at the xe2x80x9cmiddlexe2x80x9d (i.e., the portion furthest from the side and end walls of the corresponding bushing body). Significant bending stresses acting on the tip plate as the result of prolonged contact with the heavy molten material over time results in sagging due to time dependent plastic deformation, or creep. This sagging is deleterious primarily because it results in non-uniform thermal distribution and the concomitant production of fibers having substantially different diameters across the tip plate. That is, the extremes in temperature cause some bushing tips to become too cold to attenuate a fiber and others are hot enough to cause a forming instability. Both cases cause fiber breakage and a loss in conversion efficiency.
Reducing the width dimension of the plate is therefore desirable to curtail the effects of creep and increase the service life. However, the trade-off is an undesirable reduction in output and a concomitant increase in cost when only a single narrow-width tip plate is used. Also, after prolonged use, even a single narrow-width tip plate eventually suffers from creep-induced sagging, non-uniform fiber output, and increased fiber break rates.
In an effort to increase the service life of a bushing tip plate to overcome this problem and others, the present Assignee has in the past employed reinforcing members formed of platinum or a platinum alloy, termed xe2x80x9cgussets.xe2x80x9d These gussets usually extend width-wise across the upper surface of the tip plate (i.e., between the sidewalls of the bushing body) at spaced intervals, and typically have a cross-section that corresponds in shape to a xe2x80x9cTxe2x80x9d or inverted xe2x80x9cL.xe2x80x9d In use, the depending xe2x80x9clegxe2x80x9d formed by the web of each gusset is secured directly to the upper surface of the tip plate, such as by laser or tungsten-inert gas (TIG) welding.
While these gussets do serve to extend the service life of the tip plate, including even in the narrow-width case, the degree of the benefit gained is somewhat limited. In particular, the gussets having a T-shaped or inverted L-shaped cross-section are also susceptible to sagging due to bending stresses and creep as the underlying tip plate. This is because the gusset, while providing some reinforcement strength, also behaves like a simple beam, and thus experiences maximum deflection at the span midpoint as in an unsupported tip plate. In other words, despite the reinforcement, the maximum or peak stress and hence, the maximum or peak sag, still occurs at the middle of the tip plate away from the side and end walls. Accordingly, a need for an improved manner of reinforcing tip plates, including those existing bushing designs (with or without gussets) with an eye toward further extending their service life is identified.
In accordance with a first aspect of the invention, a reinforcement member for a bushing assembly having a plate-like structure including a plurality of orifices for forming fibers from a fluid material is provided. The member comprises a body including a first portion for attachment to the structure and a second portion having a profile with a variable height including at least one apex. The variable height profile and the at least one apex of the body assists in reinforcing the plate-like structure against sagging and extends the service life thereof without undue alloy usage.
In one embodiment, the reinforcement member is comprised of a single piece of material, with the body including the first and second portions having an inverted L-shaped, T-shaped, or F-shaped cross-section. The profile of the second portion of the body may have an inverted V-shaped, inverted W-shaped, or arcuate profile. Preferably, the body has a length including a midpoint, with the at least one apex located substantially at the midpoint. The midpoint may also be the midpoint between the spaced sidewalls or external support points of the bushing assembly to which a first and a second end of the body are secured.
In other embodiments, the body comprises a first member defining the first portion for attachment to the structure and a second member coupled with the first member, defining the second portion and having the variable height profile with the at least one apex. The first member may have a T-shape or an inverted L-shape in cross-section. Likewise, the second member may have a T-shape or an inverted L-shape in cross-section, and may be formed from one or more component parts. Additionally, the second portion may have an arcuate profile, an inverted V-shaped profile, or an inverted W-shaped profile, each including the at least one apex. Preferably, the second member includes a web having an end that is welded directly to an upper surface of the first member, and optionally may have a profile that defines two or more apexes. In any of the embodiments, either the first or second portion of the body may include a plurality of strategically positioned openings. These openings serve to reduce the amount of material required to fabricate the reinforcement member without compromising the strength thereof.
In accordance with a second aspect of the invention, a bushing assembly for use of forming a plurality of fibers from a fluid material at an elevated temperature is disclosed. The assembly comprises a structure having a plurality of orifices through which the fluid material passes to form the fibers and at least one reinforcement member. This member comprises a first portion for attachment to the structure and a second portion having a profile with a variable height including at least one apex. The variable height of the reinforcement member including the at least one apex enhances the ability of the structure to resist sagging and extends the service life thereof while minimizing the amount of precious metal used for reinforcement.
The fiber forming structure is typically plate-like, with different width and length dimensions to form a rectangular shape. In one embodiment, at least one reinforcement member extends along a width dimension of the plate, and preferably a plurality of independent, spaced reinforcement members extend width-wise along the plate-like structure. The fiber-forming structure also has an upper surface (the molten glass material contacts this surface) to which the first portion of each reinforcement member may be welded. Each reinforcement member may be fabricated from either a single piece of material or at least two pieces of material secured together, such as by welding.
In accordance with a third aspect of the invention, a reinforcement member portion for use in a bushing assembly having a fiber-forming tip plate including at least one existing gusset is provided. The reinforcement member portion comprises a body for attachment to the gusset and having a profile with a variable height including at least one apex. The variable height and the at least one apex of the reinforcement member portion assists in reinforcing the gusset and hence, at least the adjacent portion of the tip plate, against sagging, which extends the service life thereof while minimizing the amount of precious metal used for reinforcement.
In one embodiment, the gusset has a substantially planar upper surface and the body of the reinforcement member portion includes a web having a first end that is welded to the upper surface of the gusset. The body may have a T-shaped or inverted L-shaped cross section, and the profile of the body may be selected from an arcuate profile, an inverted V-shaped profile, or an inverted W-shaped profile.
In accordance with a fourth aspect of the invention, a method for reinforcing a structure capable of forming fibers from a fluid material supplied to a bushing is disclosed. The method comprises securing at least one reinforcement member to the structure, said reinforcement member comprising a first portion for attachment to the structure and a second portion having a profile with a variable height including at least one apex. The variable height of the reinforcement member including the at least one apex enhances the resistance of the structure to bending stresses and extends the service life thereof while minimizing the amount of precious metal used for reinforcement.
In one embodiment, the securing step comprises securing a plurality of independent reinforcement members to the structure in a spaced relationship. The reinforcement member may comprise a first member defining the first portion and a second member defining the second portion, in which case the securing step comprises securing the first member to the structure, and securing the second member to the first member. The fiber forming structure may further comprise a tip plate including at least one existing gusset, in which case said method further includes attaching the second portion of the reinforcement member to the gusset. The reinforcement member second portion thus assists in preventing both the gusset and the tip plate from sagging as the result of bending stresses and creep.
In accordance with a fifth aspect of the invention, a reinforcement member for use in a bushing assembly for forming fibers from a fluid material at an elevated temperature is provided. The bushing assembly includes a bushing tip plate having an upper surface and a plurality of strategically positioned fiber-forming orifices. The reinforcement member comprises a body having a lower portion including a web for attachment to the upper surface of the bushing tip plate and an upper portion integrally formed with the lower portion. The upper portion has a profile shaped for resisting both a bending stress created partially by the weight of the material and a creep created partially by the elevated temperature of the material over time in combination with the bending stress, and including at least one apex. The variable height profile of the body including at least one apex enhances the resistance of the bushing tip plate to sagging and thereby substantially extends the service life thereof while minimizing the amount of precious metal used for reinforcement.